1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device and a method for fabricating the same that can extend an effective channel length without changing layout.
2. Background of the Related Art
Recently, with increase of packing density of a semiconductor device, the number of cells required in the same area increases and the size of a unit device decreases. As a result, a short channel effect is enhanced and roll-off of a threshold voltage increases, so that it is difficult to control device characteristic in mass production of the product.
A related art semiconductor device and a method for fabricating the same will be explained with reference of the accompanying drawings.
FIG. 1A to FIG. 1E are sectional views illustrating fabricating process steps of a related art semiconductor device.
As shown in FIG. 1E, a related art semiconductor device includes a field oxide film 12 formed in a semiconductor substrate 11, for defining a field region and an active region, a gate 19 formed by sequentially depositing a gate oxide film 14, an amorphous silicon film 15, a diffusion barrier film 16, a metal film 17 and a mask film 18 on one region of the semiconductor substrate 11, a channel region 13 formed in the semiconductor substrate 11 below the gate 19, a lightly doped drain (LDD) region 20 formed in the semiconductor substrate at both sides of the gate 19, insulating film sidewalls 21 formed at both sides of the gate 19, and source and drain regions 22 and 23 formed in the semiconductor substrate 11 at both sides of the insulating film sidewalls 21.
A related art method for fabricating the semiconductor device will now be described.
As shown in FIG. 1A, a field oxide film 12 is formed in a semiconductor substrate 11 by a shallow trench isolation (STI) process to define a field region and an active region.
A channel ion is injected into the semiconductor substrate 11 using a mask to partially expose the semiconductor substrate 11 corresponding to the active region. The channel region 13 is then formed in the exposed semiconductor substrate at a predetermined depth.
As shown in FIG. 1B, the gate oxide film 14 is formed on an entire surface of the semiconductor substrate 11. The amorphous silicon film 15, the diffusion barrier film 16, the metal film 17 and the mask film 18 are sequentially deposited on the gate oxide film 14.
As shown in FIG. 1C, the mask film 18, the metal film 17, the diffusion barrier film 16, the amorphous silicon film 15, and the gate oxide film 14 are selectively removed by photolithography and etching processes to remain on the channel region 13 and the semiconductor substrate 11 adjacent to the channel region 13, so that the gate 19 is formed.
As shown in a portion xe2x80x98Axe2x80x99 of FIG. 1C, in the etching process, undercut occurs, in which both sides of the amorphous silicon film 15 are excessively etched. For this reason, an effective channel length of the lower parts decreases.
Also, the gate 19 having a multilayered structure consisting of the gate oxide film 14, the amorphous silicon film 15, the diffusion barrier film 16, the metal film 17, and the mask film 18 has high aspect ratio so that the semiconductor substrate 11 close to the gate 19 is shaded by the gate 19.
As shown in FIG. 1D, lightly doped impurity ions are injected into the entire surface of the semiconductor substrate 11 using the gate 19 as a mask. Therefore, the LDD region 22 is formed in the semiconductor substrate 11 at both sides of the gate 19 at a predetermined depth.
At this time, the gate 19 and the LDD region 20 do not overlap each other as shown in a portion xe2x80x98Bxe2x80x99 of FIG. 1D. This is because that the ions are not injected into the semiconductor substrate 11 at both sides of the gate 19 shaded by the gate 19 having high aspect ratio.
As shown in FIG. 1E, a nitride film is deposited on the entire surface of the semiconductor substrate 11 including the gate 19, and then etched back to remain at both sides of the gate 19, so that the insulating film sidewalls 21 are formed.
Subsequently, heavily doped impurity ions are injected into the entire surface of the semiconductor substrate 11 using the gate 19 and the insulating film sidewalls 21 as masks so that the source and drain regions 22 and 23 are formed in the semiconductor substrate 11 at both sides of the insulating film sidewalls 21 at a predetermined depth. Thus, the related art semiconductor substrate is completed.
However, the related art semiconductor device and the method for fabricating the same have several problems.
Since undercut occurs in the amorphous silicon film during the patterning process of the gate, the effective channel length decreases. For this reason, short channel effect is enhanced, thereby degrading the characteristic of a semiconductor device.
Furthermore, the source region and the drain region are not overlapped each other as a dopant is not injected into the region shaded by the gate having high aspect ratio. As a result, the semiconductor device has a serious defect.
Finally, a defect like floating of a wordline occurs as the gate exposed to the air is oxidized, so that the characteristic of a semiconductor device is degraded.
Accordingly, the present invention is directed to a semiconductor device and a method for fabricating the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a semiconductor device and a method for fabricating the same that extends an effective channel length and prevents a gate from being oxidized, thereby improving reliability of the device and production yield and increasing packing density.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a semiconductor device includes a device barrier film formed in a semiconductor substrate, for defining an active region, a channel region formed in the semiconductor substrate at a variable depth and defined by removing some of the semiconductor substrate corresponding to the active region in a groove form, and a gate electrode formed on the semiconductor substrate with a gate insulating film interposed therebetween, a material of the gate electrode being covered with the gate insulating film.
In another aspect of the present invention, a manufacturing method of the semiconductor device includes the steps of forming a device barrier film in a semiconductor substrate which defines an active region, depositing a conductive film on an entire surface of the semiconductor substrate, forming a trench by removing a conductive film to partially expose the semiconductor substrate in the active region, defining a channel region by removing the exposed semiconductor substrate in a groove form, forming a gate insulating film on surface of the semiconductor substrate including the trench, burying the semiconductor film and the cap insulating film in the trench, removing the gate insulating film formed on the conductive film, removing the conductive film to form a gate consisting the gate insulating film, the semiconductor film and the cap insulating film.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.